This invention relates to a light emitting device, and more particularly to a semiconductor laser device.
A semiconductor laser chip as a light source for optical communication or for data processing units such as digital audio disks, video disks, and so forth is discussed, for example, by Oka et al in the article entitled "Innovation of Semiconductor Laser Technique" on page 25 of the May issue of "Semiconductor World", 1982.
A prior art reference ("Semiconductor Laser Satisfying Requirements of Audio Disks" by Fushiki et al in the September 14 issue of "Nikkei Electronics", p.p. 138-152) discloses that a semiconductor laser chip (which will hereinafter be referred to also as "laser chip") can be formed by cutting (causing cleavage) of a wafer having formed thereon electrodes, with the electrode having a multi-layered metal structure using mostly gold (Au) as its principal material.
The inventor of this invention has found out that when the wafer is cut to produce the laser chips, Au as the electrode is stretched and torn off. Because of this, a part of the AU electrode hangs down in the proximity of the chip and often causes a junction short-circuit defect.
The inventor has also clarified that when the laser chip described above is produced, the electrode disposed on one surface of the laser chip is likely to swell out and to hang down for the following reasons, and hence a short-circuit is likely to develop around a p-n junction.
The laser chip has a structure in which a multi-layered grown layer is formed on a main plane of a substrate which is about 100 .mu.m thick, and in which laser light is emitted from the end surface of an active layer as one of the constituent layers of the multi-layered grown layer (more accurately, the end surface of a resonator). At least one of the electrodes is disposed on the side of the upper surface of the multi-layered grown layer. The distance between the electrode on the multi-layered grown layer and the active layer is extremely small, e.g. about 3 .mu.m. Therefore, if the electrode on the multi-layered grown layer swells out and hangs down from the periphery of the laser chip, the hanging portion of the electrode comes into contact with a region of a different conductivity type while bridging the p-n-junction, or comes into contact with the p-n junction itself, thereby causing an electric short-circuit. Since the electrode on the multi-layered grown layer is made of Au having high malleability as described already, Au is stretched and torn off when the wafer is cut, and an expanding electrode portion is unavoidably formed around the periphery of the laser chip.
The inventor has also clarified that the corners of the laser chip are likely to crack, and a short-circuit can also develop due to such a crack.